Levothyroxine

What This Medicine Does

Levothyroxine is a synthetic version of thyroxine (T4), the main hormone your thyroid gland produces. When your thyroid is underactive (hypothyroidism), your body doesn't get enough of this essential hormone.

What thyroid hormone does for you:

• Controls your metabolism and energy
• Regulates body temperature
• Supports brain function and mood
• Helps your heart beat properly
• Keeps your digestion working

Levothyroxine simply replaces what's missing - it's biologically identical to your body's own T4 hormone.

---

How to Take It Correctly

Getting levothyroxine to work properly depends heavily on how and when you take it.

The Golden Rules

1. Take it first thing in the morning - At least 30-60 minutes before breakfast

2. Use plain water only - No coffee, tea, juice, or other drinks

3. Wait to eat - Don't eat breakfast for at least 30-60 minutes after taking it

4. Be consistent - Take it at the same time every single day

5. Avoid certain supplements - See "Interactions" section below

Why the Fuss?

Levothyroxine absorption is very sensitive. Food, coffee, and other medicines can block its absorption by 30-50%, making your dose ineffective even if you're taking it correctly.

---

What to Expect: A Timeline

Week 1-2

You may start to feel:

• Slightly more energy
• Less brain fog
• Improved mood

Note: Physical symptoms like hair changes and skin improvements take longer.

Week 4-6

Your body is adjusting:

• Energy continues to improve
• Less cold sensitivity
• Better digestion
• Improved sleep

Week 6-8: The Magic Zone

This is when your doctor will check your TSH level:

• Full benefit should be apparent
• Your doctor can fine-tune your dose based on lab results
• Most symptoms should be significantly improved

Ongoing: Stable Maintenance

• Once stable, you'll have blood tests every 6-12 months
• Dose may need adjustment over time
• Pregnancy, illness, or weight changes can affect your dose

---

Signs Your Dose May Need Adjustment

Too Low (Under-replacement)

You may notice:

• Fatigue and low energy
• Weight gain or difficulty losing weight
• Feeling cold when others are comfortable
• Dry skin and hair
• Constipation
• Brain fog or depression
• High cholesterol (LDL)

Too High (Over-replacement)

You may notice:

• Rapid heartbeat or palpitations
• Feeling hot when others are comfortable
• Anxiety, irritability, or tremors
• Difficulty sleeping
• Weight loss despite good appetite
• Hair thinning
• Bone loss risk with long-term overtreatment

If you notice these symptoms, contact your doctor - a simple blood test can check if your dose needs adjustment.

---

Pregnancy: Special Considerations

If you're pregnant or planning pregnancy, tell your doctor immediately.

Why it matters:

• Thyroid hormone needs typically increase by 20-50% during pregnancy
• Your baby depends on your thyroid hormone in early pregnancy
• Low thyroid hormone can affect baby's brain development

What to expect:

• More frequent TSH testing (each trimester)
• Dose adjustments are common
• Don't adjust your dose on your own during pregnancy

---

When to Call Your Doctor

Seek Immediate Care For:

• Chest pain or pressure
• Rapid, pounding, or irregular heartbeat
• Severe headache
• Extreme anxiety or panic
• Fainting or loss of consciousness

Contact Your Doctor Soon For:

• Symptoms that your dose is too high or too low (see above)
• Planning pregnancy or positive pregnancy test
• New medications being prescribed
• Scheduled surgeries (may need dose adjustment)

---

Food & Medicine Interactions

Foods/Supplements to Avoid Within 4 Hours

These can block levothyroxine absorption:

• Calcium supplements - Take at bedtime or 4+ hours apart
• Iron supplements - Take at bedtime or 4+ hours apart
• Antacids - Wait 4 hours (aluminum, magnesium, calcium-based)
• Cholesterol medicines - Colestipol, cholestyramine (wait 4+ hours)
• Soy products - Can interfere with absorption
• High-fiber meals - May reduce absorption

Medicines That May Affect Your Levels

---

Practical Daily Tips

1. Set a daily alarm - Take your medicine at the same time each morning

2. Keep water by your bed - Take your pill immediately upon waking, then go back to sleep if needed

3. Store properly - Keep at room temperature; protect from light and moisture

4. Stick to one brand - If possible, use the same manufacturer each time (small differences between brands exist)

5. Track your symptoms - Note energy levels, weight, temperature sensitivity to discuss with your doctor

6. Don't double up - If you miss a dose, take it as soon as you remember, unless it's almost time for your next dose

---

For Healthcare Professionals

Clinical Information

Pharmacology & Mechanism

Levothyroxine (T4) is a prohormone converted to triiodothyronine (T3) by deiodinase enzymes in peripheral tissues. T3 is the biologically active form that binds nuclear thyroid hormone receptors, regulating gene expression involved in metabolism, growth, and development.

Dosing & Administration

Initial Dosing (Adults):

Administration Tips:

• Take on empty stomach, 30-60 min before breakfast
• Separate from calcium, iron, antacids by 4 hours
• Consistent timing relative to meals and other meds

Monitoring

TSH Goals:

Timing of Testing:

• Recheck TSH 6-8 weeks after dose change
• Once stable, check every 6-12 months
• More frequent during pregnancy, dose adjustments, or when interacting medications start/stop

Note: TSH has 6-8 week half-life; testing earlier than 6 weeks may not reflect new equilibrium.

Contraindications & Warnings

Contraindications:

• Untreated subclinical hyperthyroidism
• Uncorrected adrenal insufficiency (may precipitate adrenal crisis)
• Recent myocardial infarction (relative)

Warnings:

• Cardiac effects - May exacerbate angina, arrhythmias; start low and titrate slowly in cardiac disease
• Bone loss - Overtreatment associated with decreased bone density, especially postmenopausal women
• Adrenal insufficiency - Correct glucocorticoid deficiency before initiating

Drug Interactions

Agents Decreasing Levothyroxine Efficacy (separate by 4+ hours):

• Calcium carbonate, iron supplements
• Aluminum hydroxide, magnesium hydroxide (antacids)
• Sucralfate, cholestyramine, colestipol
• Soy products, high-fiber foods

Agents Affecting Thyroid Function Tests:

• Estrogen/birth control pills increase TBG → higher total T4, free T4 normal
• Androgens, glucocorticoids decrease TBG → lower total T4, free T4 normal

Agents Altering Requirements:

• Amiodarone, lithium: May induce hypothyroidism
• Phenytoin, carbamazepine, rifampin: Increase levothyroxine metabolism
• Warfarin: Levothyroxine may increase anticoagulant effect

Efficacy & Outcomes

• Restores euthyroid state in ＞95% of patients with appropriate dosing
• Improves LDL cholesterol by 7-20% in overt hypothyroidism
• Normalizes menstrual function and fertility in most women
• Pregnancy outcomes similar to euthyroid controls with adequate replacement

---

Medical Disclaimer: This content is for educational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider before starting, stopping, or changing any medication.